leetcode202 Happy Number

Write an algorithm to determine if a number is "happy".

A happy number is a number defined by the following process: Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle
which does not include 1. Those numbers for which this process ends in 1 are happy numbers.

Example: 19 is a happy number

12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 =
1

import java.util.ArrayList;
import java.util.HashSet;

public class Solution {

public boolean isHappy(int n) {
if(n<1)
return false;
if(n==1)
return true;
int last = 0;
int cur = n;
HashSet<Integer> map = new HashSet<Integer>();
while(last!=cur && !map.contains(cur)){
ArrayList< Integer> num = length(cur);
last = cur;
map.add(cur);
cur = 0;
for(int i = 0;i<num.size();i++){
cur+=(num.get(i)*num.get(i));
}

}
if(cur == last && last==1)
return true;
else{
return false;
}
}
public static ArrayList<Integer> length(int x){
ArrayList<Integer> num = new ArrayList<Integer>();
while(x!=0){
int b = x%10;
num.add(b);
x = x/10;
}
return num;
}
public static void main(String[] args) {
// TODO Auto-generated method stub
System.out.println(new Solution().isHappy(2));
}

}